Dr Liesel van der Merwe is a small animal medicine specialist. Send her your questions: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Dr Liesel van der Merwe

Cancer is becoming more common in our pets as they are living longer and veterinarians are learning more every day in how to diagnose these conditions. Animals present with the same tumours found in humans and the characteristics are also very similar.

In general, cancer is more common in older animals but some forms have a predilection for younger animals as well. In the majority of situations we do not know what causes cancer. Some, such as skin cancer, are obviously related to lack of pigmentation and sun exposure, being common on the ear tips and nose of white cats and the tummy of white dogs (fox terriers, Bull terriers and Staffordshires being common).

As an owner you may see an obvious lump developing in or under the skin, or you may present your dog or cat for a seemingly unrelated symptom and be confronted with a diagnosis of cancer.

It is important to realise that not all cancers (malignancies or neoplasia being synonyms) are equal. Some grow slowly and do not really spread to other organs. These cancers are classified as having a more benign behaviour. Cancers with a malignant behaviours can either be very rapid growing and invasive at their initial site or they may spread rapidly to other organs such as the lungs, liver and spleen.

Tumours will initially spread to the local glands, which in proper terms are called lymph nodes. The progression of cancer is more rapid in pets than in humans, as their lifespan is shorter.

The veterinarian’s first responsibility once he suspects a tumour is to try to identify the type of cancer and also to see how big it is and how far it has spread. This process is called staging and each type of tumour has different criteria by which this classification is made.

The prognosis and best treatment option depend on how the tumour is staged and this allows both you and your veterinarian to make an informed decision on whether to treat or euthanize your pet, and which treatment protocol is likely to give the best results.

In some situations surgical removal of the tumour is all that is required, in others only chemotherapy or radiation therapy is required, and some will require both surgical removal as well as additional therapies.

In many treatment situations the aim is remission and not cure. Chemotherapy conjures up awful images for most owners, as they have seen people undergo treatment.

Veterinarians will use many of the same drugs used for humans to treat pets, but the dosages are less and the regimens less intense.

In general there are very few side effects to chemotherapy in veterinary patients. Sometimes patients are a little nauseous for one or two days after treatment, but more serious side effects are extremely rare.

Owners who elect chemotherapy have to be emotionally prepared to live with the ever present threat of disease progression and also have to be dedicated to vet visits for treatments and check-ups for blood counts and other monitoring requirements.

Basically the aim should be to prolong life if possible without causing any suffering or pain for your pet, and in some situations where cancer is diagnosed this may be possible. Some common cancers in our pets include the following:

• Lymphoma (gland cancer) - amenable to treatment with good remission rates in many cases.
• Osteosarcoma (bone cancer) – common in large breed dogs and is very malignant, needing amputation and chemotherapy.
• Mammary tumours - sterilisation before the second heat, even before the first heat, dramatically decreases the incidence. Approximately half are very malignant.
• Squamous cell carcinoma (skin cancer) – a locally recurrent, invasive, sun-induced cancer. Treatment includes surgical resection, local chemotherapy and radiation.
• Mast cell tumours - these skin nodules range from benign to very malignant.
• Haemangiosarcoma (splenic tumour) - especially common in German Shepherd dogs. No real effective treatment but removal of the spleen is palliative for about three to six months.